1. Field of the Invention
The present invention relates to an article inspection device for inspecting dangerous goods, such as explosives, chemicals, biological weapons, nuclear materials and drugs, hidden in an article. In addition, the present invention also relates to an article inspection method.
2. Description of the Related Art
In order to detect dangerous goods, such as explosives, chemicals, biological weapons, nuclear materials and drugs, hidden in a ship container or in an air container, many technical solutions have been proposed, for example, two popular solutions of which are an x-ray inspection technology and a neutron inspection technology, which are simply described as follows:
1. The X-Ray Inspection Technology
a) X-Ray Transmission Solution
The conventional x-ray transmission solution includes a monoenergetic x-ray transmission method and a polyenergetic x-ray transmission method. In each of the methods attenuation information of x-rays transmitting through an article to be inspected is firstly detected by use of a transmission detector array, and then a two-dimensional image of the article is formed based on the attenuation information. The two-dimensional image is representative of mass thickness information of the article along the x-rays transmission path. In this way, by analyzing the shape of the two-dimensional image, an operator can determine whether the article contains dangerous goods therein or not. However, the x-ray transmission solution only can obtain an integration of attenuation ability of the article to be inspected along the x-rays transmission path, thereby it can not discriminate a thinner article having a high atomic number and a high atomic density from a thicker article having a low atomic number and a low atomic density. Therefore, it can not detect nuclear materials hidden in the article with enough accuracy.
b) Nuclear Resonance Fluorescence Solution
The conventional nuclear resonance fluorescence solution comprises firstly adopting x-rays to excite an atomic nucleus, and then detecting gamma photons generated by the atomic nucleus after being excited. In this way, the conventional nuclear resonance fluorescence solution can obtain “fingerprint” information of the atomic nucleus of interest. However, the x-rays that can generate resonance absorption have a very small energy spectrum width, which causes the article to generate a few number of resonance fluorescence but a great number of scattering photons after being irradiated by the x-rays, thereby the conventional nuclear resonance fluorescence solution is disadvantageously interfered by background information from the scattering photons, and has a poor inspection sensitivity. For the purpose of improving the inspection sensitivity, another method of using an adjustable monoenergetic x-ray source is recently proposed, but it needs an electron accelerator with energy of more than 100 MeV.
2. The Neutron Inspection Technology
a) Neutron Transmission Solution
The conventional neutron transmission solution is similar with the above conventional x-ray transmission solution. The neutron is sensitive to materials having a low atomic number, particularly hydrogen, but usually is not sensitive to those having a high atomic number. Thereby, compared with the above conventional x-ray transmission solution, the conventional neutron transmission solution is suitable for detecting materials containing a great deal of hydrogen. However, the neutron transmission solution also can only obtain integration information along the neutron transmission path, thereby it can not discriminate chemical elements of materials arranged at various spatial locations. Therefore, it can not detect nuclear materials hidden in the article, either.
b) Elements Concentration Analysis Solution
The elements concentratioin analysis solution can discriminate different elements based on gamma rays induced by reaction of neutrons with nuclear. Furthermore, another elements analysis solution that can discriminate different elements arranged in three-dimensional space is recently proposed, wherein a three-dimensional space element image of an article to be inspected, such as a container or a vehicle, can be formed in a 5 cm×5 cm×5 cm spatial resolution. However, the elementary analysis solution only can be adapted to nuclides having a large neutron reaction cross section, such as Nitrogen, Carbon, Oxygen and Hydrogen, and can not be adapted to nuclear elements having a small neutron reaction cross section. In addition, in the elementary analysis solution, it needs to detect energy spectra of y-rays with high temporal and energy resolution; Because of the very complicated y-rays spectra induced by the neutron reactions with matter, it is very hard to interpret spectra and extract elements concentration information. Also, the neutron generator should produce neutron pulse of nanosecond width, this is very difficult.
In addition to the above two conventional inspection methods, there are a few of other methods, for example, a nuclear quadrupole resonance (NQR) solution. The NQR method is sensitive to a molecule and can get “fingerprint” information of the molecule. But a condition must be satisfied that the molecule must contain a nucleus whose quadrupole moment is not zero and an electric field gradient in which the atomic nucleus is located must be rather large. However, only a few of materials can satisfy with the above condition. Furthermore, NQR does not work well if the inspected object is electromagnetically shielded.